Process for separating bitumen from tar sand recovered from deposits by mining

ABSTRACT

1. A PROCESS FOR SEPARATING BITUMEN AND SAND FROM TAR SAND MATERIAL RECOVERED FROM SUBTERRANEAN DEPOSITS BY MINING COMPRISING: CONTACTING THE TAR SAND MATERIAL WITH AN AQUEOUS SOLUTION COMPRISING AN INORGANIC POLYPHOSPHATE SUBSTANCE PLUS AN ALKALINITY AGENT, THE TEMPERATURE OF SAID SOLUTION BEING GREATER THAN 100* F.

C- O. WALKER PROCESS FOR SEPARATING BITUMEN FROM TAR SAND Nov. 5, 1974 RECOVERED FROM DEPOSITS BY MINING Filed June 18, 1973 United States Patent 3,846,276 PROCESS FOR SEPARATING BITUMEN FROM TAR SAND RECOVERED FROM DEPOSITS BY MINING Clarence 0. Walker, Richmond, Tex., assignor to Texaco Inc., New York, N.Y. Filed June 18, 1973, Ser. No. 371,203 Int. Cl. Cg 1/04 US. Cl. 208-11 Claims ABSTRACT OF THE DISCLOSURE A method for separating bituminous petroleum from tar sand recovered from deposits by mining. In one illustrative embodiment, the mined tar sand material is fed into a mixing container and contacted with a hot alkaline polyphosphate solution. Bitumen separates from sand without formation of an emulsion or a froth. The fluid used in conjunction with this separation technique is an aqueous solution of a polyphosphate wetting agent such as sodium acid pyrophosphate plus an alkalinity agent such as sodium hydroxide, heated to a temperature of from about 100 F. to about 200 F. The portion of bituminous petroleum dispersed in the aqueous phase is separated from the phosphate solution by contacting the fluid with a hypdrocarbon fluid such as diesel oil.

BACKGROUND OF THE INVENTION Field of the Invention This invention pertains to a method for separating and recovering bitumen from tar sand recovered from subterranean tar sand deposits.

Description of the Prior Art Petroleum is found in subterranean formations or reservoirs in which it has accumulated, and recovery of conventional petroleum is achieved by penetrating these reservoirs with wells and permitting the fluid to flow to the surface as a result of natural pressure existing in the reservoir, or by pumping the fluid to the surface in some instances where insufficient natural pressure exists to force it to flow to the surface. Many petroleum-containing reservoirs contain petroleum which is too viscous to flow or be pumped from the reservoir under normal circumstances. When such reservoirs are encountered, production is possible only by means of some process of supplemental recovery, in which energy is supplied to the reservoir in the form of heat and/or a solvent or emulsification chemicals to reduce the viscosity of the petroleum.

The most extreme example of formations which contain petroleum too viscous to be recovered by conventional means are the so-called tar sands or bitumen sands, such as those located in the Western United States, Western Canada, and Venezuela. These formations are known to contain enormous reserves of bituminous petroleum, but the bituminous petroleum contained therein is too viscous to be recoverable by conventional techniques.

The present state of the art for the recovery of bitumen from tar sand deposits can be generally classified as strip mining or in situ separation. Strip mining requires 3,846,276 Patented Nov. 5, 1974 ice removal of the overburden by mechanical means and the mixture of bitumen and sand that constitutes the tar sand deposit is then similarly removed by mechanical means and transported to a surface processing plant for separation of bitumen and sand. In situ separation processes make use of techniques for separating the bitumen from the sand within the tar sand deposit itself, so the bitumen in some modified form may be transported to the surface with the sand left in the tar sand deposit. Techniques presently employed for in situ separation may be classified as thermal or emulsification processes. The thermal techniques include in situ combustion, (fire flooding), and steam flooding. Emulsification processes also involve the use of steam plus some additional chemical to promote emulsification of the high viscosity bitumen so that it may be transported to the surface in the form of a low viscosity oil-in-water emulsion, where the emulsion is resolved into bitumen and Water.

Methods taught in the prior art for processing tar sands recovered from open pit mines or strip mines in-- clude direct coking, anhydrous solvent extraction, cold water separation techniques which make use of a wetting agent, and several hot water techniques.

The fuel costs for the direct coking technique are presently prohibitive, and the solvent cost for the anhydrous solvent technique is excessive even with solvent recovery processes.

The hot or cold water separation techniques appear to hold great promise for processing mined tar sand. Several problems have been encountered, however. Emulsion formation is almost spontaneous when bituminous petroleum contacts hot water containing an alkalinity agent such as sodium hydroxide. While formation of a stable oil-in-Water emulsion is useful in some in situ recovery processes, emulsions of both the oil-in-water and water-in-oil type are frequently formed as a by product of cold or hot water separation processes. In either case, the emulsion must be broken or resolved into its individual phases. Resolving emulsions involving bituminous petroleum is usually difficult for several reasons. Asphaltic substances are 'very effective emulsifying agents and form very stable emulsions. Furthermore, the specific gravity of bitumen is almost exactly equal to the specific gravity of water, which means there will be no gravity related forces due to density differences to aid in phase separation even if surface forces responsible for emulsification can be neutralized.

Another very serious problem which has been encountered in commercial separation projects is formation of a stable froth. The air or other gas entrained froth is very stable and quite often huge, unmanageable volumes of the froth are produced.

In view of the foregoing, it can be appreciated that there is a substantial, unfulfilled need for a surface processing method for separating bitumen or bituminous petroleum recovered from surface or subterranean tar sand deposits by mechanical means such as strip mining, which does not result in formation of an emulsion or froth.

BRIEF DESCRIPTION OF THE DRAWING The attached drawing illustrates the surface equipment involved in one illustrative embodiment of my process for separating bitumen from mined tar sands.

3 SUMMARY OF THE INVENTION I have discovered, and this constitutes my invention, that bitumen may be separated from tar sands by a technique wherein the tar sand is contacted by a hot, aqueous polyphosphate solution containing an alkaline substance such as caustic or sodium hydroxide. The tar sand is fed continually into a mixing vat Where contact with the hot alkaline polyphosphate solution occurs. The mixture is fed to a settling tank where separation into sand, bitumen and an aqueous phase having a minor amount of bituminous material contained therein occurs. The mixture is contacted with a hydrocarbon treating fluid which solubilizes the bitumen and facilitates separation thereof. Polyphosphate wetting agents suitable for use in my invention include sodium acid pyrophosphate, tetrasodium pyrophosphate, sodium trimetaphosphate and sodium tetrametaphosphate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS My invention can best be understood by referring to the attached drawing in which tar sand material which has been dug from an open pit mine and transported by mechanical means is dumped into container 1. Screw conveyor 2 conveys tar sand at a steady rate into mixing vessel 3. Vessel 3 is equipped with a stirring device 4. An aqueous solution of polyphosphate and an alkalinity agent is prepared in container 5, from which the solution is pumped by pump 6 through heat exchanger 7 where the fluid is heated to a temperature in excess of 100 F. and preferably between 100 F. and 200 F. The heated alkaline aqueous polyphosphate solution mixes with tar sand in tank 3, where the mixture is agitated by mixer 4 and then pumped by pump 8 into separation tank 9. For a continuous process, a series of separation tanks may be used in parallel, with sequential routing of the fluid to the several tanks so the mixture can remain quiesent for a period of time sufiicient to facilitate settling of sand 10 in the bottom of the tank. Most of the bitumen accumulates in a zone immediately above the sand layer. An aqueous layer forms on top, which is comprised of the hot, alkaline polyphosphate solution having a small amount of bitumen dispersed therein. Sand is removed from the lower zone in tank 9 by some means such as the screw conveyor 13 on a continuous or intermittent basis.

A hydrocarbon fluid from tank 14. is metered by pump 15 into the separation tank 9 at a predetermined flow rate. The aqueous solution and hydrocarbon treating fluid are mixed in separation tank 9 by stirrer 16. Bituminous material from the lower layer as well as from the aqueous suspension dissolves in the hydrocarbon treating fluid and forms layer 17. The treating fluid with bitumen dissolved therein is transported via line 18 to a refinery. Presence of hydrocarbon treating fluid in the bitumen aids pumping same to the refinery process unit. Separation and recovery of hydrocarbon treating fluid may be accomplished in the refinery unit. Of course, hydrocarbon treating fluid recovery may be accomplished immediately after leaving separation unit 9 if desired.

The alkaline, aqueous polyphosphate solution 19 is pumped via line 20 and pump 21 through filter element 22 to tank 5 for recycling through the separation process equipment.

The fluid used in this process is an aqueous alkaline solution of a polyphosphate such as tetrasodium pyrophosphate Na P O sodium acid pyrophosphate Na 2H2P2 07 or pentasodium tripolyphosphate, plus an alkalinity agent such as caustic soda (sodium hydroxide, NaOH).

Polyphosphates are inorganic salts whose anions contain P units linked by sharing oxygens with other tetrahedra. The polyphosphates may be in chain form, e.g. [P 0 1 1 or [P 0 1 1 or in a ring form [P O and [P 0 1 1 triand tetra-metaphosphates respectively.

Polyphosphates are hydrophilic surface active agents as opposed to organic wetting agents which may be considered hydrophobic surface active agents. There are no oleophilic moieties present in inorganic polyphosphates so they are not surfactants in the sense of alkyl or alkylaryl sulfates, sulfonates or phosphates. The prior art teaches the use of polyphosphates as builders in household detergents, and that polyphosphates function as deflocculants in drilling fluids and other suspensions, and for the purpose of forming soluble complexes.

Any Water soluble salt of pyrophosphoric acid, H P O may be used in the process of my invention. For example, the sodium, potassium or lithium salt of pyrophosphoric acid may be used. There are usually more than one salt for each cation. For example, the sodium salts are tetrasodium pyrophosphate, 'Na P O trisodium hydrogen pyrophosphate, Na HP O disodium dihydrogen pyrophosphate (known commercially as sodium acid pyrophosphate) Na H P O and sodium trihydrogen pyrophosphate, NaHgPzoq.

Other sodium polyphosphates such as pentasodium tripolyphosphate, Na P O is also known and may be used in my process. Ring polyphosphates such as sodium trimetaphosphate Na (PO and sodium tetrametaphosphate Na (PO may also be used.

Generally the preferred materials are the water soluble salts of pyrophosphoric acid, and especially sodium acid pyrophosphate or tetrasodium pyrophosphate.

The concentration of polyphosphate in the aqueous solution may be quite dilute, as low as 0.10-5.0 percent. Although concentrations greater than this may be used, there is no particular advantage in using larger concentrations, and while the cost of the material is low, economics of the process are optimized by using the lowest effective concentration.

Ordinarily an alkalinity agent will be added to the polyphosphate solution. Care should be taken to insure that the cation associated with the alkalinity agent does not form an insoluble salt with the particular polyphosphate being used. Generally, sodium hydroxide is the preferred material, although other monovalent bases such as potassium hydroxide, lithium hydroxide or ammonium hydroxide may be used also. Polyvalent bases such as calcium hydroxide should not be used.

Suflicient alkalinity agent should be added to the solution to bring the pH thereof to a value above about 10 and preferably above 12. Generally 0.105.0 percent by weight will be suflicient. One convenient means for maintaining the desired pH is to add approximately equal amounts of the alkalinity agent and the polyphosphate.

Heating the aqueous alkaline polyphosphate to a temperature in excess of F. will increase the effectiveness of this separation technique. The preferred operating temperature is from about 100 F. to about 200 F.

Any hydrocarbon fluid which will dissolve a substantial amount of bitumen may be used. Aliphatic hydrocarbons having from 4 to 20 carbon atoms such as naphtha or diesel oil may be used. Aromatic hydrocarbons including benzene, toluene and xylene are also very effective materials for use in my invention.

One attractive feature of the process of my invention is the fact that bitumen is not emulsified and no froth is formed on being contacted with the hot aqueous alkaline polyphosphate solution. Bitumen is removed eflectively from the sand but remains in a separate phase which will form a discrete layer distinct from the aqueous solution if agitation is stopped. The bitumen may be pumped to the refining process unit, the polyphosphate solution being recycled through the separation equipment.

FIELD EXAMPLE A tar sand deposit having an overburden varying from 10 to 40 feet in thickness, said deposit having an average thickness of 65 feet, is exploited by means of open pit strip mining. After stripping away the overburden, tar sand is dug from the deposit using scrapers and transported by truck to the separation process equipment. The equipment is theoretically capable of removing the tar sand at a rate of 1500 tons per hour, although actual production rate is 1000 tons per hour. The bitumen content of the tar sand is 14 percent by weight.

Separation is accomplished by using a number of units, each with a capacity of 200 tons per hour. The tar sand is fed by screw conveyor into a 5000 gallon mixing tank. An aqueous solution of 0.30 percent by weight sodium acid pyrophosphate and 0.30 percent by weight sodium hydroxide is formulated in a 1000 gallon tank and fed into the 5000' gallon tank at a rate of 1000 gallons per hour. The polyphosphate solution is heated to a temperature of 160 F. by passing through a gas fired heater prior to being added to the 5000 gallon tank.

Two separation tanks are provided for each mixing tank, so the mixing tank output is passed first to one separation tank and then to the other. Each separation tank has a volume of 3000 gallons. A screw conveyor removes sand from the bottom of the separation tank. Bituminous petroleum accumulates in a layer immediately above the sand layer, and an aqueous layer having a small amount of bitumen dispersed therein accumulates on top. Diesel oil is added to the separation tank and mixed. Bitumen from the layer immediately above the sand as well as that dispersed in the aqueous phase, dissolves in the diesel oil. After mixing is stopped, a layer of diesel oil and bitumen forms on top, which is decanted and sent to the refinery.

The aqueous sodium pyrophosphate solution is passed through a sand pack filter and then back to the pyrophosphate make up tank for recycling through the unit.

Sand from the settling tank is placed in excavations formed in earlier stages of strip mining operations.

The separation technique elfectively removes approximately 90 percent of the bitumen from the tar sand.

EXPERIMENTAL In order to verify the operability of my invention and further to determine the optimum values for the controllable parameters, the following experimental work was performed.

One hundred gram samples of tar sand obtained from the Athabasca area in Alberta, Canada were compressed into cylindrical cakes at 6000 pounds per square inch pressure. The caked samples were placed in an open container filled with the various test solutions. A motor driven mixer blade was positioned in the solution approximately 1 /2 inches from the face of the tar sand cake and rotated. The extent of disintegration of the tar sand at the end of 15 minutes was observed and this observation is reported below. In all cases the temperature was maintained at 125-130 F.

4. Water+.3% caustic soda +.3% sodium acid pyrophosphate 100% disintegrated. 5. Water+.6% caustic soda +.6% sodium acid pyrophosphate 100% disintegrated. 6. Water+.3% sodium acid pyrophosphate NH OH to yield pH of 10.8 Slight disintegration.

After disintegration of the tar sand samples, the mixtures were allowed to settle. Clean sand settled to the bottom and distinct layers of bitumen and polyphosphate solution formed. Only a slight amount of hydrocarbon was suspended in the aqueous polyphosphate solution. Addition of diesel oil to the solution solubilized the dark material, which floated to the surface and was easily separated. No emulsion or froth was formed.

While my invention has been described in terms of a number of specific illustrated embodiments, it is not so limited, and many modifications thereof will be apparent to those skilled in the related art without departing from the true spirit and scope of my invention. Furthermore, it is not my intention to be found by any particular explanation of the mechanism responsible for the benefits resulting from the application of the process of my invention. It is my intention that my invention be limited only by such restrictions and limitations as may be imposed by the appended claims.

I claim:

1. A process for separating bitumen and sand from tar sand material recovered from subterranean deposits by mining comprising:

contacting the tar sand material with an aqueous solution comprising an inorganic polyphosphate sub stance plus an alkalinity agent, the temperature of said solution being greater than F.

2. A method as recited in Claim 1 wherein the polyphosphate is a water soluble salt of pyrophosphoric acid.

3. A method as recited in Claim 2 wherein the polyphosphate is a sodium acid pyrophosphate.

4. A method as recited in Claim 2 wherein the polyphosphate is sodium trihydrogen pyrophosphate.

5. A method as recited in Claim 2 wherein the polyphosphate is trisodium hydrogen pyrophosphate.

6. A method as recited in Claim 2 wherein the polyphosphate is tetrasodium pyrophosphate.

7. A method as recited in Claim 2 wherein the polyphosphate is a potassium salt of pyrophosphoric acid.

8. A method as recited in Claim 2 wherein the polyphosphate is a lithium salt of pyrophosphoric acid.

9. A method as recited in Claim 1 wherein the polyphosphate is a water soluble tripolyphosphate salt.

10. A method as recited in Claim 9 wherein the phosphate is pentasodium tripolyphosphate.

11. A method as recited in Claim 1 wherein the concentration of polyphosphate is at least .10 percent by weight.

12. A method as recited in Claim 1 wherein the concentration of polyphosphate is from .10 percent to about 5.0 percent by weight.

13. A method as recited in Claim 1 comprising the additional step of contacting the aqueous polyphosphate solution with a hydrocarbon fluid to promote separation of residual bitumen from the aqueous polyphosphate solution.

14. A method as recited in Claim 13 wherein the hydrocarbon fiuid is diesel oil.

15. A method as recited in Claim 1 wherein the alkalinity agent is selected from the group consisting of sodium hydroxide, lithium hyrdoxide, potassium hydroxide and ammonium hydroxide.

16. A method as recited in Claim 15 wherein the alkalinity agent is sodium hydroxide.

17. A method as recited in Claim 1 wherein the concentration of alkalinity agent is from about .10 to about 5.0 percent by weight.

18. A method as recited in Claim 1 wherein the polyphosphate solution is heated to a temperature of from around 100 to about 200 F.

19. A method for separating bitumen from tar sand material comprising:

contacting the tar sand material with an aqueous solution of a polyphosphate surface active agent selected from the group consisting of water soluble salts of pyrophosphoric acid, water soluble tripolyphosphate salts and water soluble ring polyphosphates, said solution containing an alkalinity agent in amount sufficient to produce a pH above about 10, the temperature of said solution being from about 100 F. to about 200 F.

20. A method as recited in Claim 19 comprising the additional step of contacting said tar sand material and polyphosphate solution with a hydrocarbon fluid selected from the group consisting of paraflinic hydrocarbons having from 4 to 20 carbon atoms, naphtha, diesel oil, aromatic hydrocarbons, benzene, toluene and xylene, and mixtures thereof.

References Cited UNITED STATES PATENTS Kaminsky et a1 20811 Richard (I) 208-11 Langford et a1 208-11 Bauer et a1. 208-11 Coulson 208-11 Andrassy 20811 Ross et a1. 20811 Bichard (II).

CURTIS R. DAVIS, Primary Examiner 

1. A PROCESS FOR SEPARATING BITUMEN AND SAND FROM TAR SAND MATERIAL RECOVERED FROM SUBTERRANEAN DEPOSITS BY MINING COMPRISING: CONTACTING THE TAR SAND MATERIAL WITH AN AQUEOUS SOLUTION COMPRISING AN INORGANIC POLYPHOSPHATE SUBSTANCE PLUS AN ALKALINITY AGENT, THE TEMPERATURE OF SAID SOLUTION BEING GREATER THAN 100* F. 